1. Field of the Invention
This invention relates to an image transfer method and apparatus and, specifically, to an improvement therein for improving the quality of an image transferred to an image receiving medium.
2. Description of the Prior Art
Various apparatus have been used in the prior art to transfer an image from an image source to an image receiving medium. For example, a fiber optic cathode ray tube (CRT) is used to transfer an image from a graphics display terminal or a facsimile to a photo-sensitive paper medium. The image on the image source is scanned, line-by-line, and signals are generated in response thereto representative of the brightness of the image. In the above example, an electron beam generating apparatus in the fiber optic CRT, responsive to the signals from the image source, generates electron beams in response thereto, the intensity of the beams varying in accordance with the signals from the image source. The intensity-varying electron beams in the CRT are deflected from one end of the tube to the other and impinge upon the inner surface of the CRT simultaneously therewith. The image receiving medium is scrolled across the face of the fiber optic CRT, in a direction substantially perpendicular to the direction of deflection of the electron beam. The rate at which the image receiving medium is scrolled across the face of the CRT is synchronized with the rate at which the image on the image source is scanned. While the image receiving medium is being scrolled across the face of the fiber optic CRT and while the intensity-varying electron beam impinges upon the inner surface of the CRT, the image from the image source is recorded, line-by-line, onto the image receiving medium.
However, the prior art fiber optic CRT's utilized a one-line scan technique wherein the electron beam, responsive to the above-mentioned signals, scanned along one line across the inner surface of the fiber optic CRT to transfer each line of the image to the image receiving medium. Furthermore, imperfections exist on the inner faceplate of the fiber optic CRT and in the fiber optic faceplate itself. These imperfections may include any one or more of the following: the inner faceplate includes a multitude of phosphor particles and the density of the phosphor particles on the inner faceplate may vary; holes may exist between adjacent ones of said particles; burn spots may exist at various locations on the inner faceplate; and various ones of said particles may have differing emission characteristics. Fibers in the fiber optic faceplate may be irregularly distributed and may have varying transmission characteristics. When the electron beam scans along said one line and across the imperfections, blank spots or gaps appear on said image receiving medium at locations corresponding to the location of said imperfections along said one line. As a result, streaks may appear on the image receiving medium at said locations.
To further illustrate this problem with the prior art, reference is directed to FIGS. 1a and 1b.
In FIG. 1a, a faceplate of the fiber optic CRT 10 is illustrated wherein the electron beam scans along said one line 10a on the inner faceplate thereof. As a result of the imperfections which exist, after the electron beam scans along said one line, variations in image density 10b appear on the image receiving medium at positions corresponding to the location of the imperfection along said one line.
In FIG. 1b, the fiber optic faceplate 10 is again illustrated in conjunction with the one scan line 10a. The image receiving medium 10c scrolls in a direction indicated by the arrow 10d. Since the electron beam continously scans along said one line 10a and across the imperfections which exist along said one line, streaks 10e appear on the image receiving medium 10c.